A significant problem in both disk drives and testers such as optical drives, CD drives, etc. is repeatable run out (RRO) of the tracks. The primary source of the RRO is the hole in the disk being mis-centered with respect to the spiral tracks. This mis-centering causes a sinusoidal movement of the tracks at the spin frequency. In addition, if the disk is not perfectly round, this can cause RRO at multiples of the spin frequency.
One possible way to deal with the RRO is to close the tracking loop and “learn” the repeatable control signal needed to cancel the repeatable portion of the observed tracking error. This approach requires that the tracking loop be closed without benefit of the cancelling control signal. If the RRO is not too large, this approach works extremely well. However, if the disk has a badly miscentered hole or the spin rate is very high then it can be impossible to close the tracking loop in the first place.
Accordingly, there exists a need for methods, systems, and computer program products for correcting repeatable runout.